Solid state etalons with low thermally-induced optical path length change employing crystalline materials having significantly negative temperature coefficients of optical path length

Abstract

An etalon is disclosed comprising a first rutile or strontium titanate material having a first coefficient of thermal optical path length change β 1 that has a negative value, coupled with a second material having a coefficient of thermal optical path length change β 2 that is positive, and an optical path extending through the first material and the second material, such that the effective temperature coefficient of the optical path length is close to zero. Further, the total optical path length in the cavity gives a desired free spectral range of the etalon. Etalons composed of a single crystalline material are also disclosed. Such materials may include crystalline quartz.

What is claimed is:  
     
         1 . An etalon comprising: 
 a first rutile material having a first coefficient of thermal optical path length change β 1 ;    a second material having a second coefficient of thermal optical path length change β 2 ;    an optical path extending through said first material and said second material, wherein one of β 1  and β 2  is negative.    
     
     
         2 . The etalon as claimed in  claim 1 , wherein said second material includes an optical glass.  
     
     
         3 . The etalon as claimed in  claim 1 , wherein said second material includes Bk7.  
     
     
         4 . The etalon as claimed in  claim 1 , wherein said second material includes a crystal.  
     
     
         5 . The etalon as claimed in  claim 1 , wherein said second material includes a quartz.  
     
     
         6 . The etalon as claimed in  claim 1 , wherein said etalon further includes an anti-reflective coating between said first rutile material and said second material.  
     
     
         7 . An etalon comprising: 
 a first material having a first thickness d 1 , a first index of refraction n 1 , and a first coefficient of thermal optical path length change β 1 , wherein β 1 <−1.0;    a second material having a second thickness d 2 , a second index of refraction n 2 , and a second coefficient of thermal optical path length change β 2 , wherein the ratio d 1 /d 2  equals-(n 2 β 2  )/(n 1 β 1 ).    
     
     
         8 . The etalon as claimed in  claim 7 , wherein −7 >β 1 >−25.  
     
     
         9 . The etalon as claimed in  claim 7 , wherein said etalon includes BK7.  
     
     
         10 . The etalon as claimed in  claim 7 , wherein said etalon includes quartz.  
     
     
         11 . The etalon as claimed in  claim 7 , wherein said etalon includes silicon.  
     
     
         12 . An etalon including strontium titanate.  
     
     
         13 . An etalon including a rutile material and a coefficient of optical path length that is approximately zero.  
     
     
         14 . An etalon including a strontium titanate material having a negative β, a positive β material, and a coefficient of optical path length that is approximately zero.  
     
     
         15 . An etalon comprising: 
 a rutile material having a first thickness d 1 , a first index of refraction n 1 , and a first coefficient of thermal optical path length change β 1 ;    a glass material having a second thickness d 2 , a second index of refraction n 2 , and a second coefficient of thermal optical path length change β 2  , wherein the ratio d 1 /d 2  equals-(n 2 β 2  )/(n 1 β 1 ).